The present invention relates to wound paperboard tubes used for various purposes including construction forms for pouring concrete columns, winding cores for rolls of sheet materials, container bodies, and blasting tubes for lining a hole to be filled with an explosive composition.
As indicated above, wound paperboard tubes are used for a wide variety of purposes. A chief advantage of paperboard tubes over alternative tube structures such as extruded plastic tubes, seamed metal tubes, or the like, is the relatively low cost of paperboard tubes. Paperboard tubes also have a relatively high strength to weight ratio, at least when the paperboard material is at normal moisture content levels of about 6 to 12 percent. However, when conventional paperboard tubes are exposed to significant amounts of moisture, the tubes can absorb a substantial amount of moisture, which greatly diminishes the strength of the tubes. The problem of moisture-induced degradation of paperboard tubes is most severe when the tube is fully submerged in or otherwise contacted by liquid water for an extended period of time. A conventionally made paperboard tube cannot withstand being fully submerged in water for any appreciable amount of time without losing integrity.
For these reasons, when a tube structure is needed for outdoor applications or other uses in which there is a likelihood that the tube will be exposed to rain or high moisture levels, conventional paperboard tubes are not selected.
In some cases, paperboard tubes have been treated to be water-resistant so that the tubes can tolerate at least some exposure to moisture. For example, it is known to coat outer surfaces of a paperboard tube with a water-resistant coating of resin or the like, or with a coating of nano-sized particles of inorganic material such as fumed silica. However, unless all surfaces are coated completely, immersion of the tube in water is likely to result in absorption of water. Such coating is also difficult to accomplish, particularly on the inner surface of the tube, and generally requires an additional coating operation after manufacture of the tube, thereby adding to the cost and complexity of tube formation. Further, surface coatings can be subject to damage, which can compromise the moisture barrier properties of the coating.
It is also known to form concrete column construction forms from wound paperboard tubes made with highly sized paperboard plies and conventional PVA adhesive. However, the adhesive is soluble in water and hence complete immersion of the tubes in water for extended periods can lead to disintegration of the tubes when the adhesive dissolves and the plies become detached from one another.